1,720,974 research outputs found
Damage detection in bio-polyamide 11/woven basalt fibres composite laminates subjected to dynamic events
No full textVALUTAZIONE DEL COMPORTAMENTO ALL’IMPATTO DI BIOCOMPOSITI RINFORZATI CON FIBRE DI AGAVE
No full textThe growing attention on environmental issues has led to a recent research interest in eco-sustainable and renewable materials, among which biocomposites play an important role. Biocomposites are materials consisting of a matrix with low environmental impact or renewable, reinforced with natural fibres. Several research activities reported in literature, deal mainly with the static mechanical properties. Just few works are instead devoted to the assessment of their dynamic properties, such as fatigue strength, impact strength, etc. In order to give a contribution to the knowledge of the impact behaviour of green epoxy matrix biocomposites reinforced with agave fibres, in this paper a systematic study is carried out to evaluate the impact strength of different laminates (single layer, cross-ply, quasi-isotropic), by low velocity impact test. The various selected laminates, allowed to assess the effects of the main influence parameters as fibre distribution (unidirectional and random), fibre concentration and lay-up
Laser ultrasonics for defect evaluation on coated railway axles
Full text linkThis scientific paper focuses on the application of an advanced non-destructive technique for an effective inspection of railway axles. The method pertains to ultrasonic techniques, which are widely used in the railway field. The experimental investigation was carried out on simulated defects tooled near the cross section reduction of the axle, in order to simulate fatigue cracks which, due to notch effect, can trigger crack propagation and axle failure. The aim of this research activity is to evaluate how efficiently the proposed technique detects defects and to verify its applicability to axles with a black coating for protection. In view of the experimental setup, comprising a pulsed laser for ultrasonic waves generation and a continuous beam laser plus an interferometer as the receiving unit to measure surface displacements, the presence of a black coating represents a major challenge in terms of signal detection. Nonetheless, defects were detected by collecting all the waves in a B-scan map and data were processed by cross-reading A-scans and B-Scans in correspondence of each defect analysed. Results of the analysis show how very promising and robust the application of the proposed laser ultrasonics technique is in defect detection on painted railway axles
Impact behaviour and non destructive evaluation of 3D printed reinforced composites
No full textThe widespread additive manufacturing technology for producing components having complex geometries has increased the attention towards new reinforced materials, whose internal structure can be designed ad hoc on the required mechanical performance. Moreover, fused deposition modelling (FDM) technology allows the building of continuous fibre-reinforced thermoplastic composites. Due to this innovative technology, there is a lack of knowledge mainly about the impact behaviour of these materials, also considering that the main demand comes from the transportation field (automotive, aircraft, etc.), where the impact event is always possible. Thus, the aim of this research is the investigation of the impact behaviour of specimens obtained by continuous fiber fabrication technique, where Onyx and nylon white filaments were used as matrices and glass fibres for reinforcement. Onyx is a nylon mixed with short carbon fibres. An extensive non-destructive evaluation was performed on the specimens subjected to impact tests to assess the impact damage tolerance of these materials and to measure the damage extension as well. Nevertheless, considering that different non-destructive techniques were employed, the research aims also to suggest the most suitable and reliable technique to detect damage, mainly by on-site inspection
CARATTERIZZAZIONE ALL’IMPATTO DI COMPOSITI IBRIDI CARBONIO-ARAMIDE USATI PER LA REALIZZAZIONE DI COMPONENTI DI AUTOVETTURE SPORTIVE
No full textThrough a systematic experimental analysis, the impact characterization of carbon-aramid hybrid composites, typically used in the automotive sports field, has been performed. CFRP laminates object of this study have been produced by adding a hybrid foil obtained using a fabric of twill type, so-called carbon-kevlar. In order to highlight the effects of hybridisation, that is, the different properties of kevlar fibre with respect to carbon, a comparative analysis was also carried out considering a CFRP laminate with the same lay-up. The analysis of the experimental results obtained through preliminary tensile tests and subsequent low-velocity drop-weight impact tests integrated with x-ray tomography, showed that although the hybrid composite has a lower static strength than the simple CFRP, it has an increase in impact strength of up to 50%, combined with an appreciable increase in maximum impact force and mainly in resistance to surface damage
Low-velocity impact behaviour of green epoxy biocomposite laminates reinforced by sisal fibers
Full text linkDue to its good mechanical characteristics, low cost and high availability in the current market, sisal fiber is one of the most used for the manufacturing of biocomposites in various industrial fields (automotive, marine, civil construction etc.). The particular sub-fibrillar structure of the sisal fiber (similar to aramid fibers) and the corresponding anisotropic behavior detected by recent research activities, suggest that such biocomposites should exhibit also high impact strength, in such a way to permit their advantageously use also for the manufacturing of crashworthy components (bumpers, helmets, protection systems etc.), that are at the same time also eco-friendly, lightweight and cheap. Through a low-velocity impact tests campaign, integrated by computer tomography (CT) and carried out on various “green epoxy”/sisal laminates, by varying the main influence parameters such as reinforcement distribution, fiber volume fraction and lay-up, it has been detected that angle-ply laminates exhibits specific impact performances superior to those of biocomposites reinforced by other natural fibers (flax, hemp, jute, etc.), and comparable with those of the best composites specially reported in literature, so that they can be actually used to substitute the synthetic materials for the manufacture of interesting eco-friendly energy absorbing devices, that are also lighter and cheaper
First lamina hybridization of high performance CFRP with Kevlar fibers: Effect on impact behavior and nondestructive evaluation
Full text linkThe impact behavior of a carbon-Kevlar hybrid composite, widely used in sport car manufacturing, was evaluated. To highlight the hybridization effect, comparative analyses were performed with the basic CFRP laminate having the same lay-up. Tensile, bending and low velocity impact tests, followed by nondestructive inspections, highlighted that Kevlar first lamina hybridization leads to an increment in specific impact strength, up to 55%. To assess the most reliable technique to detect the impact damage, nondestructive evaluation was performed by pulsed thermography, phased array ultrasonic technique, computed tomography and digital radiography. Phased array ultrasonic technique can be considered the most appropriate technique
Titanium Lattice Structures Produced via Additive Manufacturing for a Bone Scaffold: A Review
Full text linkThe progress in additive manufacturing has remarkably increased the application of lattice materials in the biomedical field for the fabrication of scaffolds used as bone substitutes. Ti6Al4V alloy is widely adopted for bone implant application as it combines both biological and mechanical properties. Recent breakthroughs in biomaterials and tissue engineering have allowed the regeneration of massive bone defects, which require external intervention to be bridged. However, the repair of such critical bone defects remains a challenge. The present review collected the most significant findings in the literature of the last ten years on Ti6Al4V porous scaffolds to provide a comprehensive summary of the mechanical and morphological requirements for the osteointegration process. Particular attention was given on the effects of pore size, surface roughness and the elastic modulus on bone scaffold performances. The application of the Gibson–Ashby model allowed for a comparison of the mechanical performance of the lattice materials with that of human bone. This allows for an evaluation of the suitability of different lattice materials for biomedical applications
Microstructure and mechanical properties of specimens produced using the wire-arc additive manufacturing process
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